British Prime Minister David Cameron on Thursday ordered a judge-led investigation into amnesty letters sent to IRA suspects, in an apparently successful attempt to stop Northern Ireland's top politician from quitting.
The existence of the letters became public knowledge on Tuesday after one of them caused the collapse of the trial of a man accused of a notorious 1982 bombing in London by the Irish Republican Army (IRA), an anti-British paramilitary group.
Northern Ireland First Minister Peter Robinson had threatened to resign from the power-sharing executive in Belfast if Cameron's government did not announce an inquiry into the letters by Thursday night.
Just hours before Robinson's deadline, Cameron took the opportunity of a joint press conference in London with visiting German Chancellor Angela Merkel to announce that he appointed an independent judge to look into the letters.
Cameron later said the inquiry would report by May.
It emerged this week that British authorities had sent letters to about 200 fugitive republicans suspected of crimes during Northern Ireland's violent past, informing them that they will not face prosecution.
Robinson, whose Democratic Unionist Party (DUP) is drawn from the pro-British, largely Protestant communities that fought the republicans for three decades, expressed outrage at what he said were effectively secret amnesties.
"The case has already been referred to the Police Ombudsman but, as the first minister has said, we should have a full, independent examination of the whole operation of this scheme," Cameron told reporters.
The letters emerged on Tuesday when a judge ruled that John Downey, 62, a suspect in the 1982 Hyde Park bombing that killed four soldiers, should not be prosecuted for the attack because he had received an official letter while he was on the run in 2007 assuring him he would not face prosecution if he re-entered the United Kingdom.
Cameron has repeatedly said the letter to Downey was a "terrible mistake", but his government has decided not to appeal the judge's decision and seek a retrial.
The revelation has caused a storm of outrage in Northern Ireland, where power is delicately balanced between the Protestant and Catholic, largely republican communities.
"I agree with the first minister of Northern Ireland that, after the terrible error in the Downey case, it is right to get to the bottom of what happened," Cameron said.
He later sent a tweet suggesting the inquiry had mollified the first minister.
"I have just spoken to Peter Robinson. I told him I shared his anger over the Downey letter -- and was glad we have agreed on an inquiry," Cameron tweeted.